Zinc Tetrafluoroborate: A Versatile and Robust Catalyst for Various Organic Reactions and Transformations

Abstract

This account discusses the use of aqueous zinc(II) tetrafluoroborate as a mild and selective catalyst for various important organic transformations. In general, the advantages of the methodologies discussed include high yields; short reaction times; excellent regio-, chemo­-, and stereoselectivities; mild reaction conditions; and high efficiency. The use of the catalyst in a synthesis of the antihypertensive drug metoprolol is also discussed. 1 Introduction 2 Protection and Deprotection 2.1 Selective Deprotection of <i>tert</i>-Butyl(dimethyl)silyl Ethers 2.1 Tetrahydropyranylation and Depyranylation of Alcohols 2.2 Conversion of Aldehydes into Geminal Diacetates or Cyanoacetates 2.3 Selective Thioacetalization of Aldehydes 2.4 Mild and Efficient Cleavage of Oximes, Hydrazones, and Semicarbazones 3 Rearrangements of Ten-Membered-Ring Allenes 4 Organic Methodologies 4.1 Mannich Reaction of Aldimines with Silyl Enol Ethers in Aqueous Media 4.2 Synthesis of Highly Substituted Pyrroles under Solvent-Free Conditions 4.3 One-Pot Biginelli Reaction at Room Temperature 4.4 Epoxide Ring Opening with Amines and Synthesis of Metoprolol 5 Conclusions